The present invention relates generally to antennas and more particularly to a low-profile antenna suitable for inclusion in a portable, hand-held communication device, which antenna is constructed on a printed circuit board for precision fabrication, broadband operation and enhanced efficiency.
It is well understood that two- way communication apparatus, whether fixed, mobile or portable, require associated antenna devices to send and receive messages and/or other intelligent information. For portable radio units, a frequent accommodation has been to provide an external whip antenna. These antennas extend upwardly or normal to the surface of the radio unit and are made flexible to avoid injury to the radio user. Unfortunately, such exterior whip antennas add significantly to the overall dimensions, which is particularly disadvantageous where compactness is a design criteria, and, in any event, such antennas are cumbersome, unwieldy and may be uncomfortable to the user when the radio unit is worn on the person.
One solution to the foregoing is to provide a low-profile antenna for the associated radio communication device. By low-profile, it is meant that the principal radiating element is positioned essentially parallel to one of the radio unit's surfaces instead of orthogonal thereto. In point of fact, there is usually a parasitic element provided in association with the driven or radiating element. Examples of these low-profile antenna configuration may be found in U.S. Pat. Nos. 4,494,120 and also 4,584,585. In the structures as disclosed in these patents, a radiating element is located in a parallel relation to a flat surface but spaced therefrom at a predetermined distance. In each case, a parasitic element is provided in association with the driven element. While these antennas meet an important objective, i.e., low-profile, compact design, there are some aspects of their operating characteristics that are somewhat less than desired. They are formed by rod elements which may not provide the extent of the bandwidth needed for a particular application. Moreover, because of the rod element construction, and because they are spaced by supports, usually at end locations, they are susceptible during their service life to being bent out of their desired shape, or otherwise damaged, which, of course, affects their overall operating performance. Again, because of the rod element construction, they are not easily constructed or at least positioned with the desired degree of precision during manufacturing. Any deviation from the theoretical spacings and/or locations give rise to less than optimum antenna performance.
What is needed then is a simple, two-element low-profile antenna that exhibits broad band operation and a high degree of efficiency and which, nevertheless, may be manufactured with precision and repeatability with respect to the desired operating characteristics.